The invention relates to an application head for use in a device to apply liquid adhesive, especially hot-melt adhesive, to a length of material. The device permits intermittent application.
Applying molten hot-melt adhesive to lengths of material is common practice where the lengths of material are attached to a substrate. The adhesive is applied intermittently to keep the specific consumption of hot-melt adhesive low. The adhesive is applied by controllable adhesive nozzles. In order to apply the adhesive economically and uniformly, it is necessary to produce an application pattern which applies adhesive beads and interrupts the application over areas of a few millimeters. To reduce the amount of adhesive applied, by reducing the thickness of the strand of adhesive, has its limitations since the strand of adhesive may break or application may be irregular.
EP 0 474 155 A and EP 0 367 985 A2 describe application heads with a hole-type nozzle controlled by a pneumatically actuable nozzle needle. In the case of high material speeds, attempts to apply adhesive economically fail because these nozzle units cannot achieve the required cycle frequency. The cycle frequency is limited because of the mass inertia of the nozzle needle, the pneumatic cylinder and the pneumatic membrane, respectively. In addition, continuous control of the cycle frequency is often obstructed by natural oscillatory frequencies of the system.